1. Field of the Invention
The invention relates generally to a rotary power trowel machine for finishing concrete, more particularly, to a rotary power trowel having blades with controllable tilt, a gyroscopic stabilizer ring, a safety clutch mechanism for rapid disengagement of the drive mechanism if the device goes out of control, and a handle adjustable to the height of the operator.
2. Description of the Prior Art
During recent years, mechanized equipment for troweling large surface areas of concrete have been developed and used. Wet concrete is poured into a form in the construction of floors, sidewalks, highways, and the like, and is troweled during its hardening period in order to produce a smooth finished surface free of bubbles. During the finishing process, water rises to the surface of the wet concrete and evaporates while chemical reactions within the concrete cause it to harden and set. Finishing with a trowel or similar tool is believed to compact the concrete and to increase its strength. Power driven equipment is known and is in commercial use for finishing concrete more rapidly and with greater uniformity and quality of surface smoothness than is achieveable by manual troweling.
Early rotary troweling machines are disclosed in U.S. patents to Whiteman (U.S. Pat. No. 2,198,929, issued Apr. 30, 1940); Conway (U.S. Pat. No. 2,277,389, issued Mar. 24, 1942); Allen (U.S. Pat. No. 2,342,445, issued Feb. 22, 1944); Troxell (U.S. Pat. No. 2,394,274, issued Feb. 5, 1946); and McCrery (U.S. Pat. No. 2,594,331, issued Apr. 29, 1952). The McCrery patent is representative and exemplary of early rotary trowelers, and the basic design described is still used in modern conventional rotary powered trowelers. As is generally disclosed in the patents above, such trowelers typically comprise a housing, an engine enclosed within the housing, a rotatable shaft connected to the motor either directly, as in the Troxell and Conway patents, or indirectly, as in the Allen, Whiteman and McCrery patents. The rotatable shaft extends vertically downwardly from the housing and a plurality of spider arms extend between the shaft and troweling blades. A circular guard ring extending outside the periphery of the blades is supported slightly above the surface of the concrete troweled by the blades through attachment to the housing by means of stabilizer arms. A handle extends upwardly and outward from the housing and is equipped with manual controls. In operation, the engine is started, causing the troweling blades to rotate. The operator manipulates the machine through the handle along the surface of wet concrete, allowing the rotating blades to exert troweling action on the concrete surface. Initially, the troweling blades are oriented nearly parallel to the concrete surface, but as the concrete hardens, the blades can be tilted, such as in the manner provided in the Whiteman patent, to increase the effective pressure on the concrete surface brought about by the troweling blades striking the concrete surface obliquely.
These and other patents exemplifying rotary troweling machines, or components thereof, are as follows:
______________________________________ U.S. Pat. Nos.: 2,888,863 2,882,805 2,101,895 2,351,278 2,208,801 2,468,981 2,434,408 2,556,983 3,259,033 2,108,470 3,331,290 3,062,107 3,791,754 3,412,657 3,296,946 2,689,507 3,402,647 4,046,483 2,662,454 4,046,484 ______________________________________
Rotary troweling machines have used many clutching and emergency stopping methods, the simplest or most common clutch being the mechanical centrifugal clutch. On an engine which idles, the clutch is disengaged, but an engine speed increases, as controlled through an engine throttle, the centrifugal clutch engages to drive the trowel. For emergency stopping in the event the device leaves the operator's hands, a centrifugal engine kill switch, such as is exemplified in U.S. Pat. No. 3,331,290 to Harding, Jr., is used. Such a switch closes automatically to kill the engine when loss of control causes the handle to swing in a circle centered on the trowel blades. However, devices with a centrifugal engine kill switch are hazardous because in practice two complete turns of the handle generally are made before the device comes to a stop, and the operator will probably have been hit during the first revolution. Furthermore, a hazardous condition can exist when an engine so equipped is started. Upon starting the engine the centrifugal clutch will not become engaged if the initial engine speed is at an idle, and the operator can safely move from his position in starting the engine to a position to control the action of the trowel. However, if the initial engine speed is sufficiently greater than idling speed, such as could occur if the throttle setting is too high initially, the centrifugal clutch will engage the trowel before the operator assumes position to control action of the trowel. If the starting operation involves pulling a starting cord connected to the engine, the operator is in a quite vunerable position with respect to such premature engagement, and is subject to serious injury if struck by the handle.
A second method used for rotary power trowel clutching is a normally disengaged hand clutch, controlled by a lever on the handle of the device. When manually activated, the lever brings together a split sheave clutch on the engine shaft, and when the lever is released, the handle can usually be expected to stop rotating within one turn. Constructed to disengage automatically when not held by the hand of the operator on the lever, the hand clutch mechanism can be a safer method of clutching the trowel than the centrifugal clutch. However, the hand clutch in practice causes hand fatigue on the operator, particularly during prolonged operation of the device. To overcome their fatigue problem, operators have been known to circumvent operation of the hand clutch by fastening a handkerchief around the lever or using other means to continuously engage the clutch lever. When operating in such a condition, no safety control whatever exists on the device, and it could spin indefinitely out of control when so operated.
The present invention overcomes the shortcomings enumerated above by providing an improved safety clutch mechanism requiring no manual disengagement by the operator, and capable of quickly stopping a rotary power trowel out of control.
Most rotary power trowel devices have fixed trowel handles not adjustable to the height of the operator, causing physical discomfort to operators who happen to be shorter or taller than the average height for which the handle is designed. A rotary trowel is known, however, having a handle which pivots at the connecting point to the trowel gear case, held in that position by a connecting rod which is connected near the midpoint ot the handle and to the top of the engine. Such an arrangement suffers from problems incident to transmission of engine vibration directly to the handle and thus to the operator. The present invention overcomes problems of prior non-adjustable trowel handle, or trowel handles which transmit engine vibration, by providing an improved adjustable trowel handle.
Most present rotary trowels provide for tilting their blades by means of a hand knob located near the end of the control handle, such as is disclosed in the Whiteman patent (U.S. Pat. No. 2,198,929). Turning of the hand knob causes a cable or chain extending along the handle tube and exiting near the gear case to act upon a fork-like member with a horizontal rod as a pivot point to act downwardly upon a pressure plate linked in some manner to a blade tilting means. In the present invention, an improved blade tilting construction is disclosed which allows precision blade adjustment, smooth operation of the blade pitch control, and absence of blade "flopping" when the rotary trowel is lifted.
Rotary power trowels are known which employ stabilizer rings rotating near the end of the troweling arms to impart strength to the assembly. While light trowels and heavy trowels have been manufactured, the light trowels being adaptable for use with concrete which is soft, and the heavy trowels being useful when the concrete has set somewhat further, the present invention provides an attachment in the form of a heavier gyroscopic stabilizer ring. Besides providing a single machine having the versatility of two separate trowels of different weight, the gyroscopic stabilizer ring enhances trowel balance, as well as adds weight. Greater stability results from lowering of the trowel center of gravity and the gyroscopic effect it creates. Conventional methods to increase trowel weight, such as adding concrete blocks, or the like, raise the center of gravity, provide no gyroscopic effect since they do not rotate, cannot be safely secured, and result in an unbalanced, as well as hazardous, mode of operation.